Your question title is a little unclear. Is the graph actually reads VS writes? Or is it just reads and writes on the same graph.

Reads vs writes would be rather useless unless you want to see what your applications are doing more of. What you are likely seeing is reads and writes represented on the same graph. This is important, because it can show total disk usage at peak periods. If you are maxing out the disk I/O, this is where you would likely see it.